import java.util.Scanner;

public class Java20 {
    public static void main(String[] args) {
        double all=0,m,n;//  m/n
        for(int i=1;i<=20;i++){
            n=fun(i);
            m=fun(i+1);
            all+=m/n;
        }
        System.out.println(all);
    }
    public static int fun(int month){
        int m,n,i;
        m=0;n=0;
        for(i=0;i<month;i++){
            if(i<=1){
                m=1;
                n=1;
            }
            if(i>1){
                n=m+n;
                m=n-m;
            }
        }
        return n;
    }
}
